Lithium ion batteries are widely utilized as power sources for portable electronic devices. A lithium ion battery has a structure in which a positive electrode, a negative electrode, a separator and an electrolyte that includes an organic solvent are enclosed inside a hermetically sealed container. If the sealing of the container of the lithium ion battery is defective, electrolyte will leak out from the location of the defect. Therefore, lithium ion batteries are subjected to an inspection using an airtightness inspection device.
An airtightness inspection device disclosed in Patent Literature 1 includes: a two-layered storing container that is divided into a first storage section and a second storage section; a suction device that sucks out gas from inside the second storage section and decompresses the gas; a gas shutoff valve that is provided in a first communication port between the first storage section and the second storage section; and a sensor unit (gas detection means) that is provided in a second communication port. In the aforementioned airtightness inspection device, when performing an airtightness inspection, a lithium ion battery is disposed in the first storage section, the second storage section is decompressed in a state in which the gas shutoff valve is open, and the gas shutoff valve is then closed. Thereby, a gas that is inside the first storage section flows into the second storage section through the sensor unit, and at that time the sensor unit detects whether or not a solvent gas from an organic solvent that originates from the lithium ion battery whose airtightness is defective is contained in the gas. The sensor unit is constituted by a semiconductor-type gas sensor, and a cylindrical holder that holds the gas sensor in a hollow interior of the holder, in which exhaust holes are provided in the circumferential face of the holder. Thereby, gas that flows into the holder from one end of the holder that is arranged on the first storage section side turns at the front face of the gas sensor so as to move towards the exhaust holes, and flows into the second storage section through the exhaust holes.